1. Technical Field
This disclosure relates to integrated circuit devices, and more specifically, to a multiple threshold device using carbon nanotubes and techniques for forming such devices.
2. Background of the Related Art
As the dimensions of modern integrated circuitry in semiconductor chips continue to shrink, scaling down traditional semiconductor devices using known techniques has become increasingly difficult. Therefore, there has been a search for new materials and techniques to replace traditional silicon. Semiconducting carbon nanotubes have been proposed as they can conduct very high currents for their size. However, because of their small dimensions, the actual current conducted is limited to tens of microamps each. Further, the difficulty in fabricating carbon nanotube arrays has prevented widespread adoption of carbon nanotubes (CNTs) as a replacement for silicon or other traditional semiconductors as active channel materials in integrated circuit devices.
Multiple threshold devices enable desired circuit applications such as ternary logic. Most traditional computer logic is based on binary logic, i.e. 1 or 0, true or false. Ternary or higher levels of multivalued logic have attracted attention due to potential advantages in simplicity and energy efficiency in chip design as the complexity of interconnections is reduced as well as speed improvements in arithmetic processing. Also Multi-threshold CMOS (MTCMOS) is a variation of CMOS chip technology which has transistors with multiple threshold voltages (Vth) to optimize delay or power.